1. Field of the Invention
The present invention relates generally to electronic maps and geographic information, and in particular, to a method, apparatus, and article of manufacture for storing maps and geographic data on a personal digital assistant (PDA).
2. Description of the Related Art
Computer implemented geographic information systems (GIS) are known in the art. Such GIS provide for the retrieval and display of geographic information (e.g., maps). A GIS is a system of software, hardware, and data that delivers geographic data (street maps, property boundaries, power transmission lines, etc.) along with any associated attribute information. It can show you where a street is and also tell you the street name, when it was last paved, whether it is a one-way street, etc. Using a GIS, a user can perform complex queries (from a web browser to a server) to discover such things as how many people live near the street, what their income level is, and what the zoning laws are. A GIS can operate on a network/internet wherein the geographic information is stored on a server and transmitted to a client/user where the information (map picture and other data) is displayed on a web browser.
For the client to properly display the geographic information, a computer system with the appropriate processing capabilities, software, and memory is required. For example, a client may be required to utilize a computer with a web browser such as INTERNET EXPLORER or NETSCAPE and have a minimum of 10 megabytes of available memory. Additionally, to display the geographic data such that a user does not have to wait an inordinate amount of time to retrieve and load the data, an appropriate internet connection (e.g., a 28.8 Kbps modem) and a computer system with significant processing power (e.g., a minimum speed of 100 megahertz) may be required.
Field/utility technicians such as gas company employees, salespersons, plumbers, insurance adjusters, or any type of employment that requires travel to different locations, often utilize or require access to maps and geographic information. Further, such technicians often need to interact with a map to obtain relevant information. For example, a plumber/contractor may want to determine where the main gas line or water line on a street is located. However, while out in the field, the technicians often do not have a network connection, and carrying a laptop or desktop computer is cumbersome and impractical. Thus, it is desirable to have a small (handheld) portable computing device with the capabilities to display and interact with geographic information both online and offline.
Prior art handheld computing devices (also referred to as palm PCs or personal digital assistants (PDAs)), are often used to access and utilize personal information. Many handheld computing devices are available in today""s marketplace. Typically, handheld computing devices are only slightly larger than the size of one""s palm (hence, the name palm PC) and have a small display screen for viewing a plethora of items. Software can be installed on a PDA to provide enhanced functionality. For example, a personal productivity tool may be installed to provide access to a calendar, contacts, email, Internet browsing, audio books, and audio recording capabilities. Card slots may also be available to provide additional memory or other functions (e.g., a modem). Additionally, some PDAs have infrared (IR) ports for communication.
The PDA environment, however, poses several challenges for geographic information systems in terms of memory, storage, processor speeds, wireless transmission rates, and display attributes. For example, PDAs commonly only maintain 96K or less of memory, 2 Mb (megabytes) or less storage, a 13 MHz processor speed, and a black and white or gray scale display mechanism. Further, field technicians using a PDA need to view and interact with maps displayed. The low bandwidth offered by wireless transmission services, coupled with the slow processors, result in unacceptable download times. Also, the technicians in many instances work in trenches or other places where it is not possible to establish a connection to the servers (requiring offline usage).
Thus, there is a need for a geographic information system that overcomes the above described deficiencies on a portable handheld electronic device such as a PDA.
To help better understand embodiments of the invention, it is useful to describe the data utilized in prior art geographic information systems. Prior art geographic information systems display map pictures that are generated using raster data. Raster data represents a map picture with points in a grid. For example, on an X-Y axis, there may be a thousand points in the X direction and seven hundred and sixty points in the Y direction. Each of these points represents a color. For example, some computer systems enable each point to represent one of eight colors. A map picture is then created by determining a color for each point in the grid.
Each map picture is static in that portions of the map picture cannot change independently of each other. That is, a portion of a map picture cannot be modified while viewing the map picture. Thus, while a map image may contain several layers of information, the information is merely a picture with no live data. When a portion of the map picture is to be modified, queried, or to perform any GIS analysis, the browser must request more data from the main server and the entire map picture is replaced. For example, each map picture, such as one representing the United States (US), may contain several layers of information, such as states, counties, and streets. When a user is viewing a map picture of the United States and wishes to view the counties in a particular state, the map picture is replaced with another map picture that contains the additional information. Typically, the additional information is stored at a server computer and the map picture is displayed at a client computer. When the map picture that is displayed is to be modified, the additional information is downloaded from the server computer. Because this additional information is in the form of raster data, it is typically time-consuming to download.
Additionally, some computer systems display schematics generated from vector-based data in computer aided design (CAD) files. Vector-based data uses descriptions of elements of the schematic to create the schematic. For example, if the schematic contains a line segment, the CAD file describes the line segment with an endpoint and a length. Moreover, these computer systems enable users to view data in CAD files from the Internet and Intranets. For instance, when a user at a computer system wishes to view a schematic, the computer system downloads all of the data in the CAD file for that schematic from a data storage device via the Internet. The CAD file typically contains data corresponding to different levels of design of the schematic. In some instances, a user may wish to view only some of the data in the files, for example, the highest level of design of the schematic. In this case, although only a portion of data is required to display the schematic requested by the user, the computer system has already downloaded all of the data in the CAD file. Because it is time-consuming to download all of the data, it is inefficient to do so when only a portion of the data is required to satisfy a user""s request. Further, it may not be possible to download all or even a portion of the data onto a PDA.
One or more embodiments of the invention provide a schema for the storage of geographic information on a personal digital assistant (PDA). Further, embodiments provide for the differential encoding and indexing of raster and vector based data. The encoding, indexing, and storage schema provide the ability to view and interact with geographic information on a PDA.
The schema provides for the compact and performable storage of both data and metadata for raster, vector, and redlining information describing mapsets. A single database is utilized for mapset metadata and data. Timestamp/history information allows smart, incremental updates of the database. Indexing information allows compact and efficient storage and retrieval of objects and vector geometry. The schema allows a variable number of mapsets, maps, raster tiles, and geometry layers. Metadata for geometry types and redlining markup information are permitted. Additionally, geo-referencing information for raster and vector data allows objects to be displayed at the correct location on the map.
Raster data used for map display on the PDA is augmented with compact vector data. The vector data may be used for efficiently storing and retrieving the map data, allowing interactive selection, and the highlighting and querying of objects. The vectors are generalized by removing detail without losing shape information in a manner appropriate to the PDA display resolution. The object location data is differentially encoded to provide the required precision using a fewer number of bytes (2 bytes per coordinate). The vector object includes spatial indexing information, to allow for spatial filtering of objects that fall within a specified view. Thus, the invention uses cartographic generalization, encoding, and indexing to provide for compact, and efficient spatial storage structures that deal with the PDA constraints of limited storage, processing power, memory and bandwidth.